Biotin's main function as a cofactor is to transfer CO2 from one active site of an enzyme complex to another. It can also transfer C2-units .
Biotin further regulates gene expression, for instance by biotinylation of histones .
In all cases, biotin is covalently bound to its partner enzyme and serves as a CO2-carrier between bicarbonate and the acceptor substrate .
The cofactor is essential for fatty acid biosynthesis .
The biotin requirement is very low, so the only nutritional deficiency is found in patients with a diet rich in raw egg-white (avidin from raw egg white has a high affinity to biotin). Otherwise there are mainly genetic disorders, resulting from a loss of function of biotinidase (the recycling enzyme) or holocarboxylase sythetase (the biotin inserting enzyme) .
Part of the required biotin is produced by the intestinal flora . Biotinidase recycles biotin from enzymes gained from food sources . Organic acideria can result from multi-carboxylase deficiency . Other resulting diseases include neurological disorders and developmental delay .